Pillar design for conductive bump

ABSTRACT

A system and method for conductive pillars is provided. An embodiment comprises a conductive pillar having trenches located around its outer edge. The trenches are used to channel conductive material such as solder when a conductive bump is formed onto the conductive pillar. The conductive pillar may then be electrically connected to another contact through the conductive material.

This application is a divisional of U.S. patent application Ser. No.13/189,127, filed Jul. 22, 2011, and entitled “Pillar Design forConductive Bump,” which application is hereby incorporated herein byreference

BACKGROUND

Conductive pillars may be formed on a semiconductor substrate in orderto provide a physical and electrical connection point for externalconnectors. Generally, these conductive pillars are formed through a toppassivation layer of the semiconductor substrate, thereby providing anexternal connection to the active devices formed on the semiconductorsubstrate. The conductive pillars are formed in a cylindrical shape inorder to accommodate later formed connections, such as a sphericalconductive bump.

The conductive bump may be formed on the conductive pillars from aconnecting material such as solder. Typically, the conductive bump isplaced onto the conductive pillars and then heated such that theconductive bump is partially liquefied and reflows into a bump shape.Once formed, the conductive bump may then be placed into contact with aseparate substrate such as, for example, a printed circuit board oranother semiconductor substrate. After the conductive bump has beenplaced in contact, the conductive bump may again be reflowed in order tobond the conductive bump to the separate substrate, thereby not onlyproviding an electrical connection between the semiconductor substrateand the separate substrate, but also providing a bonding mechanismbetween the semiconductor substrate and the separate substrate.

However, for such a process to be reliable, the amount of conductivematerial must be precisely controlled when it is placed onto thecircular conductive pillars. If there is an excessive amount ofconductive material, there is an increased risk that conductive bumpsthat are adjacent to each other could unintentionally make contact andbridge during the reflow process, providing an undesired short-circuit.Conversely, if there is an insufficient amount of conductive material,there is an increased risk that there is not enough conductive materialto provide a sufficient connection between substrates, thereby leadingto an increased risk of a cold joint.

Additionally, the interface between the conductive bump and the circularconductive pillar is a vulnerable spot for cracks that may be initiatedby the bonding process. This vulnerability could be further aggravatedif the sidewalls of the conductive pillar is fully exposed to an ambientatmosphere and allowed to excessively oxidize, thereby increasing therisk of delamination between the conductive pillar and the underfill.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1A-1B illustrate a substrate with a conductive pillar that hastrenches in accordance with an embodiment;

FIGS. 2A-2B illustrate the placement of conductive material onto theconductive pillar and within the trenches in accordance with anembodiment;

FIGS. 3A-3B illustrate the bonding of the substrate with anothersubstrate through the conductive material in accordance with anembodiment; and

FIG. 4 illustrates a conductive pillar with asymmetrically placedtrenches in accordance with an embodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of embodiments are discussed in detail below. Itshould be appreciated, however, that the embodiments provide manyapplicable inventive concepts that can be embodied in a wide variety ofspecific contexts. The specific embodiments discussed are merelyillustrative of specific ways to make and use the embodiments, and donot limit the scope of the embodiments.

Embodiments will be described with respect to embodiments in a specificcontext, namely a conductive pillar with a conductive bump formedthereon. The embodiments may also be applied, however, to other physicaland electrical connections.

With reference now to FIG. 1A, there is shown a semiconductor die 100onto which conductive bumps 205 (not shown in FIG. 1A but illustratedand discussed in FIG. 2A below) are desired to be formed. Thesemiconductor die 100 has a first substrate 101, active devices 103,metallization layers 105, a passivation layer 107, a series ofconductive pillars 109, and trenches 111 along the sides of theconductive pillars 109. The first substrate 101 may comprise bulksilicon, doped or undoped, or an active layer of a silicon-on-insulator(SOI) substrate. Generally, an SOI substrate comprises a layer of asemiconductor material such as silicon, germanium, silicon germanium,SOI, silicon germanium on insulator (SGOI), or combinations thereof.Other substrates that may be used include multi-layered substrates,gradient substrates, or hybrid orientation substrates.

The active devices 103 are represented in FIG. 1 as a single transistor.However, as one of skill in the art will recognize, a wide variety ofactive devices such as capacitors, resistors, inductors and the like maybe used to generate the desired structural and functional requirementsof the design. The active devices 103 may be formed using any suitablemethods either within or else on the surface of the first substrate 101.

The metallization layers 105 are formed over the first substrate 101 andthe active devices 103 and are designed to connect the various activedevices 103 to form functional circuitry. While illustrated in FIG. 1 asa single layer, the metallization layers 105 are formed of alternatinglayers of dielectric and conductive material and may be formed throughany suitable process (such as deposition, damascene, dual damascene,etc.). In an embodiment, there are at least four layers of metallizationseparated from the first substrate 101 by at least one interlayerdielectric layer (ILD), but the precise number of metallization layers105 is dependent upon the design of the semiconductor die 100.

The passivation layer 107 may be formed on the metallization layers 105over the active devices 103 in order to provide protection from physicaland environmental harm that exposure may cause. The passivation layer107 may be made of one or more suitable dielectric materials such aspolymers, silicon oxide, silicon nitride, low-k dielectrics such ascarbon doped oxides, extremely low-k dielectrics such as porous carbondoped silicon dioxide, combinations of these, or the like. Thepassivation layer 107 may be formed through a process such as chemicalvapor deposition (CVD), although any suitable process may be utilized,and may have a thickness between about 0.5 μm and about 5 μm, such asabout 9.25 KÅ.

The conductive pillars 109 may be formed to provide conductive regionsfor contact between the metallization layers 105 and an external device301 (not shown in FIG. 1 but illustrated and discussed below withrespect to FIG. 3A) such as printed circuit boards or othersemiconductor dies in, e.g., a flip-chip arrangement. The conductivepillars 109 may be formed by initially forming a photoresist (not shown)over the passivation layer 107 to a thickness greater than about 20 μm,or even greater than about 60 μm. The photoresist may be patterned toexpose portions of the passivation layer 107 through which theconductive pillars 109 will extend. Once patterned, the photoresist maythen be used as a mask to remove the desired portions of the passivationlayer 107, thereby exposing those portions of the underlyingmetallization layers 105 to which the conductive pillars 109 will makecontact.

After the passivation layer 107 has been patterned, the conductivepillars 109 may be formed within the openings of both the passivationlayer 107 as well as the photoresist. The conductive pillars 109 may beformed from a conductive material such as copper, although otherconductive materials such as nickel, gold, or metal alloy, combinationsof these, or the like may also be used. Additionally, the conductivepillars 109 may be formed using a process such as electroplating, bywhich an electric current is run through the conductive portions of themetallization layers 105 to which the conductive pillars 109 are desiredto be formed, and the metallization layers 105 is immersed in asolution. The solution and the electric current deposit, e.g., copper,within the openings in order to fill and/or overfill the openings of thephotoresist and the passivation layer 107, thereby forming theconductive pillars 109. Excess conductive material outside of theopenings may then be removed using, for example, a chemical mechanicalpolish (CMP).

After the conductive pillars 109 have been formed, the photoresist maybe removed through a process such as ashing, whereby the temperature ofthe photoresist is increased until the photoresist decomposes and may beremoved. After the removal of the photoresist, the conductive pillars109 extend away from the passivation layer 107 a first distance d1 ofbetween about 5 μm to about 50 μm, such as 40 μm. Optionally, a barrierlayer 113 may be formed over the conductive pillars 109 by, for example,electroless plating, wherein the barrier layer 113 may be formed ofnickel, vanadium (V), chromium (Cr), and combinations thereof.

However, as one of ordinary skill in the art will recognize, the abovedescribed process to form the conductive pillars 109 is merely one suchdescription, and is not meant to limit the embodiments to this exactprocess. Rather, the described process is intended to be merelyillustrative, as any suitable process for forming the conductive pillars109 may alternatively be utilized. For example, forming the passivationlayer 107 to a thickness greater than its eventual thickness, formingthe conductive pillars 109 into an opening of the passivation layer 107,and then removing a top portion of the passivation layer 107 such thatthe conductive pillars 109 extend away from the passivation layer 107may also be utilized. All suitable processes are fully intended to beincluded within the scope of the present embodiments.

FIG. 1B illustrates a top-down view of one of the conductive pillars 109along line 1-1′ in FIG. 1A. As illustrated, the conductive pillar 109may be shaped in order to act as a buffer for the amount of conductivematerial 201 (not illustrated in FIG. 1B but shown and discussed withrespect to FIG. 2A below) that will be placed onto the conductive pillar109. In particular, the conductive pillar 109 may be shaped in order toact as a reservoir of conductive material 201, such that the conductivepillar 109 can retain any excess conductive material 201 (if there istoo much conductive material 201) or else supply conductive material 201(if there is a shortage of conductive material 201) during a bondingprocess.

In an embodiment, the conductive pillars 109 may be formed with a seriesof trenches 111 or grooves alongside the outer circumference of theconductive pillars 109. These trenches 111 may be formed as a singletrench or as a plurality of trenches. If there is a plurality oftrenches 111, the trenches 111 may be formed symmetrically around theouter circumference of the conductive pillars 109 or, alternately, theymay be formed asymmetrically around the outer circumference of theconductive pillars 109 as desired. In the embodiment illustrated in FIG.1B, there are four trenches 111 formed symmetrically around the outercircumference of the conductive pillars 109.

The trenches 111 may be formed in such as fashion so that the capillaryforces between the conductive pillar 109 and the conductive material 201passively guides the conductive material 201 into the trenches 111. Forexample, in an embodiment utilizing copper as the conductive pillar 109and utilizing solder as the conductive material, the conductive pillar109 may be formed to have a first diameter d₂ of between about 10 μm andabout 100 μm, such as about 80 μm, while the trenches 111 may be formedin a curved rectangular shaped as illustrated in FIG. 1B, with a firstdepth d₃ of between about 1 μm and about 10 μm, such as about 5 μm, anda first width w₁ of between about 3 μm and about 30 μm, such as about 20μm.

However, as one of ordinary skill in the art will recognize, the preciseshape of the trenches 111 is not limited to the curved rectangular shapedescribed above and illustrated in FIG. 1B. Any other suitable shapethat provides sufficient capillary forces in order to passively guidethe conductive material 201 into the trenches 111 may alternatively beutilized. For example, a half-circle shape, a triangular shape, are-entrant cavity shape, or the like, may alternatively be utilized.

The shaping of the conductive pillars 109 may be performed withadditional process steps, but may also be performed without therequirement for any extra processing steps. For example, the trenches111 may be formed into the conductive pillars 109 by forming the desiredshape into the same photoresist that is utilized to mask and etch thepassivation layer 107 during the formation of the conductive pillars 109as described above with respect to FIG. 1A. However, any other suitableprocess, such as initially forming the conductive pillars 109 with acylindrical shape and then separately forming the trenches 111, may alsobe utilized to form the trenches 111 into the conductive pillars 109.

FIG. 2A illustrates a cross-sectional view of the semiconductor die 100after a conductive material 201 has been placed onto the conductivepillars 109 and a reflow process has been performed on the conductivematerial 201. The conductive material 201 may comprise a material suchas tin, or other suitable materials, such as silver, lead-free tin, orcopper. In an embodiment in which the conductive material 201 is tin,the conductive material 201 may be formed by initially forming a layerof tin through such commonly used methods such as evaporation,electroplating, printing, etc., to a thickness of between about 10 μmand about 30 μm, such as about 15 μm.

Once the conductive material 201 has been formed on the conductivepillars 109, a reflow process may be performed to transform theconductive material 201 into conductive bumps 205. In the reflow processthe temperature of the conductive material 201 is raised to betweenabout 200° C. and about 260° C., such as about 250° C., for betweenabout 10 seconds and about 60 seconds, such as about 35 seconds. Thisreflow process partially liquefies the conductive material 201, whichthen pulls itself into the desired bump shape due to the conductivematerial's 201 surface tension.

Additionally, this same surface tension of the conductive material 201,in conjunction with the capillary forces between the conductive material201 and the conductive pillar 109, will also guide the conductivematerial 201 into the trenches 111 over the passivation layer 107 alongthe outer circumference of the conductive pillar 109. The conductivematerial 201 may be pulled into the trenches 111 enough to fill thetrenches 111 all the way down to the passivation layer 107 (asillustrated in a first region labeled 207), or else may be pulled onlypart of the way into the trenches 111 (as illustrated in a second regionlabeled 209).

Once within the trenches 111, the surface tension of the conductivematerial 201 keeps the conductive material 201 controlled by thetrenches 111. This passive control is exerted even to some conductivematerial 201 that is located outside of the trenches 111, as the surfacetension of the conductive material 201 will shape the conductivematerial 201 into a bulge that extends outward from the trenches 111 (asillustrated in FIG. 2B below) a second distance d₄ between about 1 μmand about 15 μm, such as about 10 μm. By this process, the trenches 111can act as a reservoir for conductive material 201 by essentiallystoring excess conductive material 201 in the trenches 111 along thesides of the conductive pillars 109, even if the excess conductivematerial 201 stored is larger than the actual volume of the trenches 111themselves.

FIG. 2B illustrates an expanded top-down view of one of the conductivepillars 109 along line 2-2′ in FIG. 2A after the reflow process. Duringthe reflow process excessive conductive material 201 is passively guidedinto and fills the trenches 111 along the outer circumference of theconductive pillar 109. As discussed above, the trenches 111 may controleven more conductive material 201 than may fit within the trenches 111,as the surface tension of the conductive material 201 allows theconductive material 201 to extend beyond the first diameter d₂ of theconductive pillar 109 bulge out of the confines of the trenches 111while still being passively controlled by the trenches 111.

By passively guiding the conductive material 201 into the trenchesduring the initial reflow process, excess conductive material 201 may bestored, thereby reducing the possibility of excess conductive material201 bridging with an adjacent conductive pillar 109. Additionally, byguiding excess conductive material 201 along the sidewalls of theconductive pillar 109, the excess conductive material 201 may alsoreduce the area of the sidewalls that is exposed and which may beoxidized, thereby reducing the chance of delamination.

FIG. 3A illustrates a cross-sectional view of the semiconductor die 100after the semiconductor die 100 has been bonded to an external device301. As illustrated, the external device 301 may be similar to thesemiconductor die 100, with an external substrate 303, external activedevices 305, external metallization layers 307, an external passivationlayer 309, and external conductive pillars 311 with external trenches313. However, the external device 301 is not limited to anothersemiconductor die, and may include other devices, such as a printedcircuit board, a packaging substrate, or any other suitable device thatprovides a desired connection to the conductive pillars 109 through theconductive material 201.

In an embodiment in which the external device 301 is similar to thesemiconductor die 100, the conductive bumps 205 (not shown in FIG. 3Abut illustrated and described above with respect to FIG. 2A) are alignedand placed in physical and electrical contact to the external conductivepillars 311 on the external substrate 303. Once the conductive material201 is in physical contact with the external conductive pillars 311, abonding process may be performed. The bonding process may includeraising the temperature of the conductive material 201 so as to againreflow the conductive material 201 while simultaneously applying apressure. The reflow allows the conductive material 201 to bond to theexternal conductive pillars 311, thereby bonding the semiconductor die100 to the external device 301.

During the bonding process, the trenches 111 in the conductive pillars109 act as a reservoir through which conductive material may be suppliedto the conductive bumps 205 or else removed from the conductive bumps205. For example, if there is excess conductive material 201 formed inthe conductive bump 205, this excess conductive material may passivelybe guided into the trenches 111 during the reflow and bonding process,thereby reducing the possibility of an undesired bridge between adjacentconductive pillars 109. Additionally, if there is not enough conductivematerial 201 in the conductive bump 205 to form a bond to the externalconductive pillars 311 (which would normally lead to a cold joint),extra conductive material 201 that was stored in the trenches 111 may bepassively pulled from the trenches 111 to supply additional conductivematerial 201 to the conductive bump 205, thereby helping to prevent acold joint from occurring.

Additionally, because the trenches 111 break up the normally cylindricalshape of the conductive pillars 109, the forces applied to theconductive pillars 109 by the surface tension of the conductive material201 are applied unevenly to different parts of the conductive material201. For example, the surface tension of the conductive material 201 mayapply a force to the conductive pillars 109 around the trenches 111different from a force applied to the conductive pillars 109 that is notlocated around the trenches 111. This difference in forces may provide aself-alignment during the bonding and reflow process by imparting arotational force to the conductive pillars 109 and the externalconductive pillars 311 until the trenches 111 within the conductivepillars 109 and the external trenches 313 within the external conductivepillars 311 are aligned with each other. This rotational force helps tocorrect or reduce any potential errors in alignment or alignmentmismatch by helping to align the conductive pillars 109 and the externalconductive pillars 311.

FIG. 3B illustrates an expanded top-down view of one of the conductivepillars 109 after the reflow and bonding process along line 3-3′ in FIG.3A in which the trenches 111 supplied extra conductive material 201 tothe conductive bump 205. As illustrated, additional conductive material201 has been removed from the trenches 111 and added to the conductivebump 205 (not shown in FIG. 3B but illustrated in FIG. 3A above). Such aremoval may, but does not have to, result in a reduction of the bulge ofconductive material 201 (as seen in FIG. 2B above) such that theconductive material 201 is completely contained within the trenches 111.

FIG. 4 illustrates another embodiment in which the trenches 111 aroundthe periphery of the conductive pillar 109 may be placed in anasymmetric pattern. For example, the trenches 111 around the conductivepillar 109 may be placed a third of the way around the circumference ofthe conductive pillar 109 such that they are not mirror images of eachother on opposite sides of the conductive pillar 109. By placing thetrenches 111 asymmetrically around the conductive pillar 109, therotational forces between the conductive pillars 109 and the externalconductive pillars 311 (see, e.g., FIG. 3A above) may be enhanced, andthe self-alignment between the conductive pillars 109 and the externalconductive pillars 311 may be increased, further helping to correct orreduce any potential errors in alignment or alignment mismatch betweenthe conductive pillars 109 and the external conductive pillars 311 whenthey are bonded together.

In accordance with an embodiment, a semiconductor device comprising afirst substrate and a conductive post extending away from the firstsubstrate is provided. The conductive post comprises one or moretrenches perpendicular to the first substrate.

In accordance with another embodiment, a semiconductor device comprisinga passivation layer located over a substrate is provided. A conductivepost extends through the passivation layer, the conductive post havingan outer circumference, and a plurality of grooves is located around theouter circumference of the conductive post. A conductive material islocated over the conductive post.

In accordance with yet another embodiment, a method of manufacturing asemiconductor device comprising forming a first conductive pillar withone or more trenches over a substrate, the one or more trenches beingperpendicular to the substrate, is provided. Conductive material isplaced onto the first conductive pillar, and the conductive material isreflowed such that a portion of the conductive material is passivelyguided into the one or more trenches.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. For example,the materials used for both the conductive pillars and the conductivematerial may be modified while still remaining within the scope of theembodiments. Additionally, the exact shape of the trenches formed withinthe conductive pillars may also be modified while still remaining withinthe scope of the embodiments.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present embodiments, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present embodiments. Accordingly, the appended claims are intendedto include within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method of manufacturing a semiconductor device,the method comprising: forming a first conductive pillar with one ormore trenches over a substrate, the one or more trenches having alongitudinal axis that is perpendicular to the substrate; disposingconductive material into the one or more trenches of the firstconductive pillar; after disposing conductive material into the one ormore trenches, placing a second conductive pillar in contact with theconductive material; and after placing the second conductive pillar,reflowing the conductive material to bond the second conductive pillarto the first conductive pillar using the conductive material, whereinthe reflowing causes a portion of the conductive material within the oneor more trenches to flow toward the second conductive pillar, whereinthe conductive material self-aligns the first conductive pillar to thesecond conductive pillar.
 2. The method of claim 1, wherein thereflowing the conductive material further forms an extension of theconductive material beyond a diameter of the first conductive pillar. 3.The method of claim 1, wherein the forming the first conductive pillarwith the one or more trenches further comprises forming two or moretrenches symmetrically around the conductive pillar.
 4. The method ofclaim 1, wherein the first conductive pillar comprises copper.
 5. Themethod of claim 1, further comprising forming a barrier layer over thefirst conductive pillar before disposing the conductive material intothe first conductive pillar.
 6. The method of claim 1, wherein the firstconductive pillar extends through a passivation layer over thesubstrate.
 7. A method of manufacturing a semiconductor device, themethod comprising: forming a first conductive post with one or moretrenches over a substrate, the one or more trenches extending at leastfrom a passivation layer disposed over the substrate to an end of thefirst conductive post opposite the substrate; placing conductivematerial onto the first conductive post; reflowing the conductivematerial such that a first portion of the conductive material isretained within the one or more trenches; after reflowing the conductivematerial, placing a second conductive post in contact with theconductive material; and after placing the second conductive post,reflowing the conductive material to form a bond between the firstconductive post and the second conductive post, wherein the reflowingremoves at least some of the first portion of the conductive materialfrom the one or more trenches to the bond.
 8. The method of claim 7,wherein the conductive material is solder.
 9. The method of claim 7,wherein the one or more trenches comprises four trenches.
 10. The methodof claim 7, wherein the conductive material fills the one or moretrenches over the substrate.
 11. The method of claim 7, wherein theconductive material only partially fills the one or more trenches overthe substrate.
 12. The method of claim 7, wherein the conductivematerial extends past an outermost circumference of the first conductivepost prior to placing the second conductive post.
 13. A method ofmanufacturing a semiconductor device, the method comprising: forming afirst conductive pillar extending through a passivation layer and havinga first longitudinal groove and an outer circumference; placingconductive material onto the first conductive pillar; performing a firstreflowing of the conductive material such that capillary forces betweenthe first conductive pillar and the conductive material passively guideat least a portion of the conductive material into the firstlongitudinal groove, wherein the conductive material extends to thepassivation layer and the conductive material extends past the outercircumference of the first conductive pillar; after performing the firstreflowing, placing a second conductive pillar in contact with theconductive material; and after placing the second conductive pillar,performing a second reflowing of the conductive material to bond thesecond conductive pillar to the first conductive pillar, wherein thesecond reflowing removes some of the conductive material from the firstlongitudinal groove.
 14. The method of claim 13, wherein the conductivematerial self-aligns the first conductive pillar and the secondconductive pillar during the second reflowing.
 15. The method of claim13, wherein the conductive material is solder.
 16. The method of claim13, wherein the first conductive pillar extends through a passivationlayer, wherein the conductive material extends to the passivation layerafter the first reflowing.
 17. The method of claim 13, wherein the firstconductive pillar only has four longitudinal grooves.
 18. The method ofclaim 17, the first conductive pillar further comprising: a secondlongitudinal groove; a third longitudinal groove; and a fourthlongitudinal groove, wherein the first longitudinal groove, the secondlongitudinal groove, the third longitudinal groove, and the fourthlongitudinal groove are disposed symmetrically around the outercircumference of the first conductive pillar.
 19. The method of claim13, wherein the first conductive pillar is copper.